Lamp changer mechanism and control circuit therefor responsive to both light emission and filament continuity



Aug. 25, 1964 G. A. CAMPBELL 3,146,375

LAMP CHANGER MECHANISM AND CONTROL CIRCUIT THEREFOR RESPONSIVE T0 BOTH LIGHT EMISSION AND FILAMENT Filed Feb. 24. 1961 CONTINUITY 3 Sheets-Sheet l g a y A l I EQE /fz I. --.l

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LAMP CHANGER MECHANIsN ANO CONTROL CIRCUIT TREREEOR RESPONSIVE TO BOTH LICHT EMISSION ANO FILAMENT CONTINUETY Filed Feb. 24, 1961 :s sheets-sheet s /f INVEN TOR.

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United States Patent O 3,146,375 LAMP CHANGER MECHANISM AND CONTRL CIRCUIT THEREFR RESPUNSTVE T) RUTH LIGHT EMlSSlQN AND FELAWNT CUNTENUHY George A. Campbell, Pompton Plains, NJ., assignor to Wallace Tiernan Inc., Belleville, NJ., a corporation of Delaware Filed Feb. 24, 1961, Ser. No. 9l,508 6 Claims. (Cl. 315-89) This invention relates to a mechanism for automatically changing electric lamps employed in signal devices, and to the control means for such lamp changers. More particularly, the invention relates to a lamp changing system for signal devices which are relatively inaccessible, such as those employed as navigational aides.

Automatic lamp changers of the type shown in United States Patent 2,054,013 to C. F. Wallace have had a long record of dependable service in many types of signal lanterns throughout the world. By providing spare lamps, which are immediately and automatically available to replace burned out units, the service periods between visits to lanterns and buoys has been greatly extended with the corresponding savings in operating and maintenance costs. Lamp changers heretofore in service employed a low resistance relay coil in series with the lamp in service in order to sense lamp filament failure and initiate changer action. The prior systems, therefore, Suder a voltage drop across the relay coil with the result that full battery voltage is not available at the lamp contacts. Furthermore, it has been necessary to select and install various shunts in parallel with a relay coil to accommodate different sized lamps. The conventional lamp changer also suffers the defect that it will continue its lamp changing action when all the lamps are burned out until it fails mechanically or until the battery is eX- hausted.

It is, therefore, the primary purpose of the invention to provide a lamp changer which eliminates the stated defects inherent in conventional changers, and which, moreover, embodies additional improvements and advantages.

It is an object of the invention to provide an extremely simple transistorized lampy monitoring circuit to sense lamp filament failure and to initiate lamp changer action.

It is a further object of the invention to provide a lamp failure sensing circuit whose operation depends on the integrity of the lamp filament rather than on the flow of current through the lamp as in prior lamp changing devices.

It is still a further object of the invention to provide a lamp changer designed to rapidly and accurately move a new lamp into operative position following lamp failure.

An additional object of the invention is to provide a lamp changer control system in which power is supplied to the changer control circuit continuously, and independently of the flasher characteristic of lamp flashing mechanism ordinarily associated with lamp changing equipment.

Further, it is an object of the invention to provide a lamp changing control system which will automatically terminate changer action following a predetermed number of lamp changing attempts.

It is another object of the invention to provide a lamp changing control system which is protected against destructive run-down and at the same time prevents batteries from being exhausted following failure of all lamps in the changer.

Another object of the invention resides in the provision of a lamp changing system in which resistances, coils, or voltage dropping components in the changer control circuit are eliminated, whereby full battery voltage ICC is available at the lamp terminals. Further, it is a purpose of the invention to provide a control circuit for a lamp changer which is independent of lamp size or amperage with the consequence that selective choice of shunts, etc., is not required.

It is still a further purpose of the invention to provide a lamp changer control circuit which is designed to operate selectively at either of two nominal voltage ranges.

Signal lamps are commonly powered by air depolarized batteries which have a high initial voltage which tends to burn out lamp filaments at a high rate during the initial part of the service period. This condition dictates that the number of lamps available in a changer be increased in order to maintain continuity of service throughout the life of the batteries.

It is, therefore, another object of the invention to increase the reserve lamp capacity of the changer. The provision of a greater number of lamps in the changer permits the deliberate overloading of the lamps to increase their candle power output, without decreasing the period between service visits.

In a commercial embodiment of the invention, the lamp changer has a rotary turret adapted to hold a plurality of incandescent lamps for successive registration in an energizing circuit as the turret is rotated, a motor for rotating the turret, a motor circuit and a source of electrical energy for the lamps and the motor circuit, all as in said Wallace patent. An important point of departure from said prior changer lies in the improved control circuit which, in the commercial embodiment according to this invention, is connected between the motor circuit and the energy source by which changer action is controlled. This control circuit includes a device for gating electrical energy from the energy source to the motor circuit, and first and second alternative monitoring means in the control circuit which are responsive to the operative condition of the lamp filament for blocking passage of electrical energy through the gating device to the motor circuit. The first alternative monitoring means is responsive to light emission from the lamp and the second alternative monitoring means is responsive to the electrical continuity of the lamp filament. As and if the lamp condition alternates between the energized and the nonenergized states, the two monitoring means are alternately effective in monitoring the operative status of the lamps.

These and other objectives of the invention will be evident from a reading of the following detailed description which is presented in light of the drawings, and in which:

FIG. l is a rear elevational view of the lamp changer herein, a rear cover plate having been removed to show underlying structure and a part of the casing having been broken away to show otherwise hidden elements;

FIG. 2 is a side elevational view of the changer with parts thereof broken away to reveal underlying structure and other parts being shown in section;

FIG. 3 is a fragmentary plan view of the changer with parts broken away to show underlying structure;

FlG. 4 is a diagram of the electrical control circuit; and

Ful-GS. 4A and 4B represent modifications of the control circuit of FIG. 4.

As shown in FiGS. l and 2, the lamp changer mechanisrn herein includes a housing lil in which the changer drive mechanism and the control circuit therefor are enclosed, and a rotary turret l2 which is adapted to hold a plurality of lamps; the turret being connected to the housing liti by a turret shaft 14.

The ultimate power applied to the turret shaft ld for rotating the turret 12 is derived from a suitable motor la herein shown as a solenoid ratcheting motor suitably mounted within the housing lil. The solenoid ratcheting motor may be replaced by any other type of motor suitable for driving the turret. FIGURE 4B suggests the use of a small electric motor 16e. The motor 16 consists of a coil 18 and an L-shaped armature Zit which is connected at one end to the coil by a pivot 22 about which the armature can rock. The free end of the armature 2t) which constitutes the short leg of the L extends downwardly at the end of the solenoid and into the path of the flux which is set up when the coil is energized. A plate 24 is attached to the upper face of the armature 20 and extends outwardly beyond the armature pivot such that one end of a return spring 26 can be attached to the plate. The opposite end of the return spring 26 is attached to a bracket 28 extending laterally from the solenoid structure. Thus, the return spring 25 will bias the armature 26 upwardly about its pivot point 22, as viewed in FIG. l. When the coil 18 is energized, the armature 2i) will be pulled downwardly against the tension of the return spring 26.

The motor 16 drives a main drive worrn and the latter drives a worm gear 32 fixed to a counter shaft 34. The counter shaft 34 is mounted in a pair of adjustable sleeve bearings 35 and 37 mounted in the side walls of the housing 10. A pair of lock nuts 39 and 41 maintain the respective bearings 35 and 37 in proper adjusted position. A bevel gear 43 on the counter shaft 34 is engaged with a bevel gear 45 on the turret shaft 14- and thereby power is delivered to the turret shaft by which the turret is rotated. A second worm 36 on the counter shaft 34 drives a reset shaft 38 by way of a second worm gear fifi. Gear ratios are selected so that approximately ten turns of the counter shaft 34 are required for one turn of the reset shaft 38.

In operation, each stroke of the armature 29 picks up one tooth on a ratchet wheel 42, advancing it and thereby rotating the main drive worm 3i). rl`he motion of the armature 2t) is transmitted to the ratchet wheel 42 by means of a ratchet drive wire 44 which is V-shaped to provide an apex at which it is connected to the armature plate 24. The ratchet drive Wire has a pair of upstanding diverging legs 44a and 4411. The legs 44a of the ratchet drive wire extend through a guide slot in a guide bracket 46 in which they are free to move as the armature Z6 is oscillated. The legs 4411 of the ratchet drive drive wire 44 are joined at the top to form a closed loop which engages the teeth of the ratchet wheel 42 to operate the ratchet wheel as above described when the coil of the motor 16 is energized. Rotation of the ratchet wheel 42 is stabilized by means of a V-shaped pawl spring 48 which has one end in contact with the ratchet wheel teeth and the other end in Contact with the housing 1t?. The pawl spring is supported by a stud G extending outwardly from the face wall of the housing.

The free end of the armature 2t) interrupts flow of current into the coil 1S of the motor by opening a contact 52 on each excursion of the armature. The Contact 52 is mounted on a trip lever 54 which is mounted for rocking movement on a trip lever mounting stud 56 extending outwardly from the face wall of the housing. An oblique ear 53 is formed in the trip lever and is so disposed that the free end of the armature will engage the same each time the armature is operated by energization of the coil 18. Thus, each time the armature reaches its full stroke position, the contact 52 is opened and flow of current to the coil 18 is interrupted. Upon interruption of current to the coil 18, the return spring 26 will return the armature to its inactive position, wherein the contact 52 is closed and the circuit to the coil is again re-established. Thus, a rapid oscillation of the armature is produced when power is fed to the motor 16.

The trip lever 54 is under the influence of a spring 60 which is mounted between a spring mounting stud 6.?. and an extension 64 of the trip lever. The trip lever extension 64 has a surface 66 which is in the path of a stop pin 68 extending outwardly from the reset shaft 33. When the reset shaft is rotated sufficiently to bring the stop pin 68 into Contact with the surface 66 of the trip lever extension, the trip lever will be rotated about its pivot shaft 56 in a clockwise direction such that the contact 52 will be opened and current to the motor coil 18 will be cut off. As stated above, the gear ratios employed are such that about eight cycles of the turret 12 will result in a single revolution of the reset shaft 3S. Accordingly, the changer action will be continued until the turret is rotated through about eight cycles before the stop pin 68 will operate to open the motor circuit at the contact 52. Thus, a dirty contact in tl e lamp circuit may be wiped clean and a good lamp, otherwise inoperative, may be brought into use.

An indexing contact 7) (FIG. 3) is located at the front of the housing 1t) and is connected into the changer circuit by means of a leaf spring 72 and a binding screw 74 which extends through the face wall of the housing 1t). From the foregoing, it can be seen that all drive gears and moving parts, with the exception of the lamp turret, are enclosed within the housing and are thus protected from the elements.

The turret 12 has eight positions at which lamps may be supported and connected into the changer circuit. rl`he lamps ordinarily utilized are S-S and S-ll single contact prefocused base lamps which include a radial base flange having therein a plurality of bayonet slots by which they may be mounted on a lamp mounting contact. The turret 12 as well as the housing 1t) embodying a simplified design to permit the molding of these parts from polyester resin molding compounds.

The turret 12 is provided with eight lamp sockets in its peripheral surface. These sockets are open for the reception of lamps at the face of the turret adjacent the housing. Each socket provides supporting surfaces 76 for the lamp flange which is part of a lamp base engaging groove 78 at the front face of the turret. Associated with each lamp mounting socket is a radially disposed lamp mounting strip 89 which is attached to the inner face of the turret. The mounting strips have an inturned end from which projects a lamp mounting contact 82. The lamp mounting contact 32 is adapted to engage in one of the bayonet slots of the lamp flange which, when turned, will engage the flange under the enlarged head of the lamp mounting contact 82. A contact spider 84 mounted on the hub of the turret has formed therein eight spring contacts 86, such that a spring contact will extend outwardly into each lamp socket and contact the base of a lamp mounted therein, holding the lamp flange firmly up against contact 82 and support surface 7 6.

As shown in FIG. 2, the turret shaft 14 extends forwardly through a housing journal 38 and the turret 12 is mounted on the forwardly extending end of the shaft by means of a clutching assembly 90. The free end of the turret shaft 14 is supported in a front plate 92 which is attached to a forwardly extending housing base flange 94.

The reset shaft 38 extends rearwardly through a rear housing cover plate 96 where it has attached thereto a reset knob 98. The worm gear 46 is frictionally mounted on the reset shaft 38 by means of a reset clutch assembly 100, so that the reset shaft 38 can be manually rotated by turning the reset knob 98 for the purpose of relocating the stop pin 68 without also rotating the entire turret.

The presently preferred changer control circuit is shown in FIG. 4. Interconnection between the principal circuit components are carried by a printed circuit board 102 (FIG. 2) which is adapted to seat in a recess provided in the rear cover 96. The terminals of the board-carried circuits are brought out into the pins of a block 104 which is mounted on the inner face of the board. The pins of this block engage a miniature socket 106 mounted within the housing 10. External connections are made through the socket by way of binding posts 163, 110 and 112.

The monitoring circuit takes advantages of that characteristic of transistors which holds them olf or in the non-conducting state so long as the base is held at the same potential as the emitter.

In most auxiliary equipment, such as lamp iiashing mechanisms with which the present lamp changer is designed to operate, the positive battery terminal is connected to one terminal of a lamp 118 through a timer operated switch 128. The other terminal of the lamp is connected directly to the negative battery terminal which is usually ground. An NPN type of transistor is suited to the conditions specified. Therefore, it may be assumed that the transistor 122 in FIG. 4 is an NPN transistor. A Sylvania type 2N-ll02 transistor is suitable. If the lamp terminal were connected directly to the positive supply voltage with the switch in the negative battery connection, a PNP type transistor would be used and such other changes in the circuit would be effected as apparent to one skilled in the art to obtain the monitoring functions taught herein.

In FIG. 4, a diode or rectifier 124 is connected so as to block current flow into the base of the transistor 122 when the tiasher circuit (switch 120) is closed. The diode 124 may be type lN-91 manufactured by General Electric Company. A 100 rnfd. storage capacitor 126 is connected across the base-emitter terminals of the transistor 122 and a biasing resistor 128 (24K, `1/2 watt) connects the base terminal to the positive battery terminal.

A photoconductive light sensitive cell 135 is connected across the base-emitter terminals of the transistor 122 in parallel with the capacitor 126. A photoconductive cell suitable for the purpose is type CDS-lO manufactured by Jem Electronics Corporation. The light sensitive cell 138 is located in a recess 132 formed in the top wall of the housing 18 (FIGS. 1 and 2). The recess is in line with the lamp socket when the socket is properly positioned and thereby it is able to sense the light emission of a lamp in service. The resistance of the cell 136 is low when illuminated, e.g., 300 to 400 ohms, whereas in the dark, the resistance may be as high as 1 megohm. The combination of the lamp lilament and the photoconductive cell 130 connected in shunt across the emitter-base of the transistor provides alternate ways of monitoring the condition of the lamp in the changer mechanism. When switch 128 is open, the lamp is off and the electrical continuity of the filament is monitored. When switch 120 is closed, the lamp is on and light emission is monitored. Changer operation is initiated almost immediately upon burn out or breakage of the lamp filament and changer operation is halted immediately when a good lamp is brought into position. This assures accurate placement of the lamp 118 within the lantern assembly.

Resistors 134 (120 ohms,'1/2 watt) and 136 (100 ohms, 1/2 watt) complete the basic monitoring circuit and all that remains is to `connect the base-emitter of a second transistor 138 across the load resistor 134 in the collector of the transistor 122. The second transistor 138, which may be a Delco type 2N-553, PNP transistor, need only be large enough to deliver the required power to the coil 18 of the motor 16.

The changer motor 16 is connected into the collector circuit of the transistor 138 along with a resistor 148 (33 ohms, 3 watt) and the Contact 52 which, it will be remembered, is the contact carried by the trip lever 54 of FIG. l. It will also be remembered that opening and closing of the contact 52 produces a rapid oscillation of the armature 28 when power is fed through the transistor circuit, and this oscillation is used to rotate the changer mechanism through the ratchet wheel 42, as described.

The circuit also includes a surge limiting device across the motor coil 18. This device is shown in FIG. 4 as a diode 142, which may be a General Electric Company type 1N-91. A more economical expedient to which resort may be had, if desired, is a resistor 144 (330 ohms, 1/2 watt) as shown in FIG. 4A. Whether the diode 142 or the resistor 144 is employed, the inductive voltage surge upon opening of the contact 52 is reduced to a value less than the voltage rating of the transistor 138.

The circuit is designed to operate at 6-8 volts D.C. but it is also desirable that the circuit be operable at 12-15 Volts D.C. In order to adapt the system for operating at either of these nominal voltage ranges, the resistor 140 which is included as part of the load in the collector circuit of the transistor 138 approximately doubles the impedance in the load circuit so that when this resistance is included in the circuit, the circuit is optimum for 12-15 volts. When the resistance 140 is shorted out, -the circuit is conditioned for operation at 6-8 volts. Provision is made for by-passing the resistance 140 by resort to a shorting washer 146, which is diagrammatically shown in FIG. 4 and which is physically shown in FIG. 2. As seen in FIG. 2, the washer is seated in a recess in the rear cover 96 and it is held against the printed circuit board 102 and between appropriate circuit points thereof, i.e., the terminals of the resistance 184 by means of a screw 148. The washer is conductive on one side only, the other side being of insulating material. Thus, conditioning of the circuit for operation at either of the two nominal voltage ranges is effected simply by mounting the washer on the printed circuit board with the insulating face in contact therewith if the resistance 148 is to be active in the circuit or with the conductive face in contact therewith if the resistance is to be by-passed.

Operation Assume that the lantern assembly in which the lamp changer is mounted is in its off period. Assume further that night or dark conditions prevail, that the changer has just been placed in service, that a good lamp with intact filament is in its proper operating position in the Changer, and that the reset knob 98 has been rotated to its reset position. Under these conditions, the timer operated switch 128 will be open, the contact 52 will be closed, and the lamp iilament is intact to provide an electrical path through the lament of the lamp 118 and the contact '78 to the diode 124. When the direct current battery supply is now connected, current may ow in the various parts of the circuit as follows:

(1) A path is established from the positive side of the battery through the biasing resistor 128 to the diode 124, to the photosensitive cell 130, and to the base terminal of the transistor 122. The diode current will flow through the contact 78 and through the filament ofthe lamp 118 to the negative side of the battery. Since the diode 124 presents a very low resistance to the iow of current in this direction, most of the current through the resistor 128 will take this path. Some current will also reach the negative side of the battery through the photosensitive cell 130 directly, and through the transistor 122 by way of the emitter resistor 136.

(2) Current may flow from the positive side of the battery through the collector resistor 134 to the collector of the transistor 122 and thence through the transistor to the diode 124, to the photosensitive cell 138, through the emitter resistor 136 and from these components to the negative side of the battery.

(3) Current may also iiow from the positive side of the battery through the output transistor 138, to the solenoid coil 18, through the closed contact 52 and to the negative side of the battery.

The condenser 126 acts merely as a storage element to delay or retard changes in the voltage appearing across the base-emitter terminals of the transistor 122. This Voltage controls the action of the changer circuit.

Under the initial conditions assumed above, the base of :the transistor 122 is connected directly to its emitter through the diode 124, contact '70 and the filament of the lamp 118. These elements are each of such low resistance that they present what amounts to a short circuit across the emitter-base of the transistor 122 which thereby eliectively holds the transistor in its oli or non-conducting condition. In this state, practically no current flows through the collector resistor 134.- and this, in turn, holds the base of the transistor 138 at the same potential level as its emitter, consequently it too, is held off and the changer circuit is dormant. Current drain through all circuit components at this time is very low, usually less than one-half ma. and is due largely to leakage through the transistor 138.

The photosensitive cell 131i plays practically no part in the functioning of the circuit under the initial conditions above stated, since its resistance is more than the forward resistance through the diode 124 and, therefore, it is not a significant factor in determining the base-emitter potential of the transistor 122.

Should the filament of the lamp 118 be broken under the foregoing conditions (or should the contact 70 fail to establish a circuit due to dirt, corrosion, etc.) the circuit will operate as follows:

The circuit which connected the base of the transistor 122 directly to its emitter is broken. As soon as this happens, the current through the resistor 128 which formerly found its way back to the negative side of the battery through the diode 124 and the filament of the lamp 118, begins to charge the condenser 126 and the base of the transistor 122 starts to swing more positive with respect to its emitter. This action continues until a limiting condition is reached as determined by the value of the bias resistor 128 which is so selected that the transistor 122 is fully on. Current now ftows through the collector resistor 134 and the resulting voltage drop across resistor 134 turns the transistor 138 on as its base swings more negative with respect to its emitter.

Current through the transistor 138 flows through the solenoid coil 1S attracting the armature 29 which rotates the ratchet wheel 42, as previously explained, and thereby advances the ratchet wheel ft2 one or more teeth, depending upon its adjustment. As soon as the armature approaches the end of its initial stroke, it strikes the contact arm 52 which interrupts the circuit through the solenoid 16 by opening of the contacts 52, as above explained. When this happens, the spring (FIG. 1) returns the armature to its starting position, picking up one or more ratchet wheel teeth as it does so. Since the contact 52 is now reclosed, the cycle is repeated until the circuit at the contact 52 is opened by the stop pin 63 or until the changer is turned off when an intact filament of a new lamp recloses the input circuit through the lamp 118.

A diode 142, as in FIG. 4, or a resistance 144 as in FIG. 4A, may be connected across the coil of the solenoid to reduce the inductive voltage spikes from the solenoid to a value sufficiently low as not to damage the transistor 138. When the input circuit is reclosed through a new lamp filament, the condenser 126 will discharge virtually instantly back to its short circuited condition such that both transistors are turned off quickly. Therefore, the lamp is accurately positioned in the changer assembly at the instant the contact '70 closes the input circuit.

The foregoing discussion of the circuit operation has, as stated, assumed that darkness prevailed, and that, therefore, the photosensitive cell 13th was not illuminated. Under daylight conditions, a somewhat different situation prevails. During daylight hours, the resistance of the photosensitive cell 130 is low enough to hold the transistor 122 offf even though the filament circuit through the lamp should be broken or otherwise interrupted. In this case, the changer will not operate until the ambient light level reaching the photosensitive cell 130 falls to a low level, e.g., 10 foot candles.

The description of the circuit operation to this point assumed that the timer operated switch 120 has been open. It remains to be seen how the circuit will operate when the timer operated switch 120 is periodically closed and opened such as would occur when using a timing motor to flash the lamp on and off at regular intervals, eg., 0.5 second on and 3.5 seconds off Let it be assumed that it is night time (otherwise the photosensitive cell 13) would hold the transistor 122 in its off condition). Under these conditions, there will be a large initial surge of current through the cold filament of the lamp 118 as the switch 12@ closes. This current will fall quickly to the rated value of the lamp as the filament reaches incandescence. It will be evident that during this on period of the lamp 11S, the full value of the direct current supply voltage appears across the lamp terminals and that the current flowing through the bias resistor 12S will no longer pass through the diode 124 but that it will seek other paths. Two such paths are available. The first of these is to the condenser 126 which will start to charge up and tend to make the base of the transistor 122 more positive. The second path is through the photosensitive cell 136 to the negative side of the battery. lf the resistance of the photosensitive cell 130 is low, the base potential of the transistor 122 will not become positive enough to conduct and the changer will remain inoperative. Since the photosensitive cell 139 is so positioned in the changer mechanism, as above explained, that it is in the illumination of the lamp 118, its resistance is low enough when the lamp 118 is illuminated to clamp the transistor 122 in its ofi condition.

if, while the switch 120 is closed, the integrity of the filament in the lamp 113 is destroyed such that the filament circuit is opened, the photosensitive cell 130, by reason of the darkness, will have a very high resistance such that it can no longer hold the transistor 122 of." Within a few seconds after such lamp failure, the condenser 126 will have charged up through the resistor 128 so as to make the base of the transistor 122 sufficiently positive to conduct fully and turn the changer mechanism 0o. The changer will now operate to rotate a new lamp into the position of the one that failed. If the new lamp is a good one, the changer will turn off practically instantly as soon as the new lamp lights up.

It is now evident that the photosensitive cell 130 plays a vital part in the proper operation of the changer control circuit, particularly when working with flashing lamps which have a long on period, or with lamps which burn continuously. The importance of this portion of the circuit is underscored by a consideration of how it would operate if the photosensitive cell 130 were eliminated. It has been pointed out that during the on period of the lamp 118, the condenser 126 is charged through the resistor 128. Eventually, no matter how large the condenser 126 may be, it would charge up enough to turn the transistor 122 on and start the changer which would then rotate the lamp out of position even though the lamp were operating perfectly.

It can be seen, therefore, that the inclusion of the photosensitive cell 13) in the base circuit of the transistor 122, for the purpose described, has very definite and marked advantages. By resort to this circuit, the changer control circuit uses a small condenser which is a matter of importance since space is at a premium in the lamp housings. Furthermore, the lamps are very accurately positioned due to the quick turn off. Power consumption is significantly reduced because there is no chance for the transistor 122 to swing positive enough to approach full conduction during fiash periods of the lamp. The lamp failure sensing circuit is practically insensitive to voltage changes, and therefore no adjustment is required to accommodate this part of the circuit to different operative voltages. Finally, the entire circuit is independent of the flash characteristic and the current rating of the lamps.

It can be seen, therefore, that the invention provides alternative lamp monitoring means. One alternative, consisting of the light sensitive element 130 and the circuit which it controls, is effective when the lamp is energized. The other alternative, comprising the diode 124 in series with the lamp filament, is effective when the lamp is not energized. As and if the lamp condition alternates between the energized and non-energized states, the two monitoring systems are alternately effective in monitoring the operative status of the lamp.

While the fundamentally novel features of the invention have been illustrated and described in connection with a specific embodiment of the invention, it is belived that this embodiment will enable others skilled in the art to apply the principles of the invention in forms departing from the exemplary embodiment herein, and such departures are contemplated by the claims.

What is claimed is:

1. A control System for a lamp changer comprising a source of unidirectional electrical energy, incandescent lamp means including filament means energizable from said source, a control circuit, means responsive to a preselected voltage level in said control circuit for inhibiting a control effect, first means for establishing said voltage level during periods when the lamp is energized, and second means for establishing said voltage level during periods when the lamp is not energized, said first means being responsive to light emission from said lamp and said second means being responsive to electrical continuity of said filament.

2. In a lamp changer having a rotary turret adapted to hold a plurality of incandescent lamps for successive registration in an energizing circuit as said turret is rotated; a motor for rotating said turret, a motor circuit, a source of unidirectional electrical energy, incandescent lamp means in said turret including a filament energizable from said source of electrical energy, a control circuit connected between said motor circuit and said source of electrical energy, means in said control circuit for gating electrical energy from said energy source to said motor circuit, means responsive to the emission of light from said filament for blocking passage of electrical energy through said gating means to said motor circuit, and means responsive to the operative condition of said filament for blocking passage of electrical energy through said gating means to said motor circuit.

3. In a lamp changer having a rotary turret adapted to hold a plurality of incandescent lamps for successive registration in an energizing circuit as said turret is rotated; a motor for rotating said turret, a motor circuit, a source of unidirectional electrical energy, incandescent lamp means in said turret including a filament energizable from said source of electrical energy, a control circuit connected between said motor circuit and said source of electrical energy, a transistor for gating electrical energy from said energy source to said motor circuit, and first and second means in said control circuit responsive to the operative condition of said filament for blocking passage of electrical energy through said transistor to said motor circuit, said first means being a photo-conductive device responsive to light emission from said lamp and said second means being a diode responsive to electrical continuity of said filament.

4. In a lamp changer having a rotary turret adapted to hold a plurality of incandescent lamps for successive registration in an energizing circuit as said turret is rotated; a motor for rotating said turret, a motor circuit, a source of unidirectional electrical energy, incandescent lamp means in said turret including a filament energizable from said source of electrical energy, a control circuit connected between said motor circuit and said source of electrical energy, a transistor for gating electrical energy from said energy source to said motor circuit, and first and second means responsive to the operative condition of said filament for holding said transistor at cut-off thereby blocking passage of electrical energy through said transistor to said motor circuit, said first means being responsive to light emission from said lamp and said second means being responsive to the electrical continuity of said filament.

5. A control system for a lamp changer having a source of unidirectional voltage and a plurality of incandescent lamps including filaments energizable from said voltage source mounted in a rotary turret for successive connection of the filaments thereof with said voltage source as said turret is rotated, a periodically operated circuit breaker between said voltage source and a lamp connected therewith, a motor for controlling rotation of said turret, a control circuit connected to between said motor and said voltage source, a transistor in said control circuit for gating operating voltage from said voltage source to said motor, a light sensitive element responsive to light radiation from an incandescent filament of a lamp connected with said voltage source and across the base-emitter terminals of said transistor whereby said transistor is maintained non-conductive when said circuit breaker is closed and a lamp in said voltage source is energized, and a diode connected in series with said lamp filament and with said transistor whereby said transistor is maintained non-conductive when said circuit breaker is open and a lamp having an operative filament therein is nonenergized.

6. In a lamp changer having a rotary turret containing a plurality of electric lamps adapted to be placed successively into an operative position in an electric circuit as said turret is rotated, a control circuit adapted to detect the failure of a lamp in said operative position, a circuit breaker, a turret rotating motor under control of said control circuit adapted to rotate said turret when said control circuit detects the failure of a lamp in said operative position, a shaft rotated by said motor, circuit breaker operating means frictionally mounted on said shaft for rotation therewith into contact with said circuit breaker whereby said circuit breaker is operated and said control circuit is deenergized to limit the number of revolutions of said turret, and means for resetting said circuit breaker operating means by rotation thereof on said shaft independent of the rotation of the latter.

References Cited in the file of this patent UNITED STATES PATENTS 2,258,575 MacKay Oct. 7, 1941 2,557,531 Blanchet June 19, 1951 2,892,966 Smyth June 30, 1959 2,998,545 Smyth Aug. 29, 1961 

1. A CONTROL SYSTEM FOR A LAMP CHANGER COMPRISING A SOURCE OF UNIDIRECTIONAL ELECTRICAL ENERGY, INCANDESCENT LAMP MEANS INCLUDING FILAMENT MEANS ENERGIZABLE FROM SAID SOURCE, A CONTROL CIRCUIT, MEANS RESPONSIVE TO A PRESELECTED VOLTAGE LEVEL IN SAID CONTROL CIRCUIT FOR INHIBITING A CONTROL EFFECT, FIRST MEANS FOR ESTABLISHING SAID VOLTAGE LEVEL DURING PERIODS WHEN THE LAMP IS ENERGIZED, AND SECOND MEANS FOR ESTABLISHING SAID VOLTAGE LEVEL DURING PERIODS WHEN THE LAMP IS NOT ENERGIZED, SAID FIRST MEANS BEING RESPONSIVE TO LIGHT EMISSION FROM SAID LAMP AND 